> The decline in NO2 was modest though notable, with a − 0.41 parts-per-billion change in annual average. Lol, so they are proposing that a non-significant drop of 0.41 parts per billion of NO2 is causing a ~1.6% drop in hospitalizations due to asthma. The number of possible confounding variables here is massive, for example, the standard deviation of the number of EVs is roughly the same as the value (2013: 1.4, SD2.1 and 2019: 14.7, SD 14.7), so the ~95%CI EV penetration could be (+/- 2SD) ~ 2013: [-3.2 - 5.6], 2019 [-14.7 - 44.1]. Now obviously, the EV penetration can't be negative, so it's not going to be a "normal" distribution, but there is a wide variance across their area. This study seems to be a survey of some sort, the link they supply to the data in the abstract is a 404, so no help there. Quick skim of the abstract analysis of this paper leads me to conclude that it is likely poo quality. If their hypothesized cause (NO2) does not change in a statistically significant manner, you cannot make a claim of a statistically significant effect from it.